A letter has been published showing Nick Clegg was warned not to jettison the snoopers' charter by the director of public prosecutions.
The development comes after a poll showing high public support for more draconian surveillance techniques if they help reduce terrorism.
"For cases such as counter-terrorism, organised crime and large-scale fraud, I would go so far as to say that communications data is so important that any reduction in capability would create a real risk to future prosecutions," Keir Starmer wrote to Clegg, before the deputy prime minister ruled out a snoopers' charter.
The director of public prosecutions stressed that the current legislative framework had failed to keep up with technological changes.
The emergence of the letter is a shot in the arm to those who want the government to revive the communications data bill in the wake of the Woolwich attack.
The bill – dubbed the snoopers' charter by the press – would give intelligence agencies access to people's web browsing history, email exchanges and social media activity.
Supporters say agencies would only know of the existence of messages and when they were sent – so-called meta data – rather than the content, although there are question marks around whether the technology can be limited in that way.
The letter, which was published in the Sun, came to light after an opinion poll conducted by YouGov for the Huffington Post showing the public are generally sympathetic to the prospect of a snoopers' charter.
Thirty eight per cent of respondents said the proposals went too far but 43% were happy with the plans.
Interestingly, women were more sympathetic than men. Female respondents backed the plans by 55% to 30%, while men backed it by 48% to 46%.
That is a reversal of polling on military engagements, which men typically support more than women.
Civil liberties issues rarely poll strongly with the public and the snoopers' charter results are actually more limited than those conducted during New Labour's time in power.
When Tony Blair proposed 90-day pre-charge detention for terror suspects, for instance, only 22% of people opposed it.
Voters also appeared comfortable with the idea of UK agencies working with US agencies to retrieve data about British citizens, with 46% saying they were "pleased that the UK security services are getting information that might help them track down criminals and terrorists".
Thirty-nine per cent of respondents said they were "sorry that the UK agencies might be getting round British law to undermine our right to privacy".
The result may depend on wording. Previous YouGov polling for Liberty found that perceptions of effectiveness are vital to the way voters respond to questions about civil liberties and surveillance.